Differences in Resolution of mwr -Containing Plasmid Dimers Mediated by the Klebsiella pneumoniae and Escherichia coli XerC Recombinases: Potential Implications in Dissemination of Antibiotic Resistance Genes

Abstract

Xer-mediated dimer resolution at the mwr site of the multiresistance plasmid pJHCMW1 is osmoregulated in Escherichia coli containing either the Escherichia coli Xer recombination machinery or Xer recombination elements from K. pneumoniae. In the presence of K. pneumoniae XerC (XerC Kp ), the efficiency of recombination is lower than that in the presence of the E. coli XerC (XerC Ec ) and the level of dimer resolution is insufficient to stabilize the plasmid, even at low osmolarity. This lower efficiency of recombination at mwr is observed in the presence of E. coli or K. pneumoniae XerD proteins. Mutagenesis experiments identified a region near the N terminus of XerC Kp responsible for the lower level of recombination catalyzed by XerC Kp at mwr. This region encompasses the second half of the predicted ␣-helix B and the beginning of the predicted ␣-helix C. The efficiencies of recombination at other sites such as dif or cer in the presence of XerC Kp or XerC Ec are comparable. Therefore, XerC Kp is an active recombinase whose action is impaired on the mwr recombination site. This characteristic may result in restriction of the host range of plasmids carrying this site, a phenomenon that may have important implications in the dissemination of antibiotic resistance genes.

Small Plasmids Harboring qnrB19 : a Model for Plasmid Evolution Mediated by Site-Specific Recombination at oriT and Xer Sites

“…Recombinant plasmids pPBR1 and pPBR2 were generated by ligating HindIII-digested pPAB19-1 or pPAB19-2 to HindIII-digested pUC19 (38). Dimers of plasmids pES and pKS492 were used as controls in dimer resolution experiments (4). E. coli DS941 (AB1157 recF143 lacI q lacZ; possesses wild-type xerC, xerD, argR, and pepA) (33), E. coli DS9028 (DS941 xerD3::fol) (30), and the hyper-recombinogenic E. coli JC8679 (DS945 recBC sbcA) (32) were used to carry out the Xer recombination experiments.…”

OXA-24 Carbapenemase Gene Flanked by XerC/XerD-Like Recombination Sites in Different Plasmids from Different Acinetobacter Species Isolated during a Nosocomial Outbreak

“…These results show that during the outbreak there was no exchange of a common plasmid carrying the bla OXA-24 gene among the strains isolated. On the (3,4,13,15). Recombination occurs via formation of a heterotetrameric complex in which each recombinase catalyzes the exchange of one pair of DNA strands in a reaction that proceeds through the Holliday junction intermediate.…”

“…The accessory proteins bind the accessory sequence and induce formation of a synaptic complex that is required for recombination (3). These recombination events are involved in site-specific integration and excision of lysogenic genomes, transposition of conjugative transposons, termination of chromosome replication, and plasmid stability (3,14,16).…”

fpr , a Deficient Xer Recombination Site from a Salmonella Plasmid, Fails To Confer Stability by Dimer Resolution: Comparative Studies with the pJHCMW1 mwr Site

“…The efficiency of Xer-mediated dimer resolution at mwr when Escherichia coli is cultured in L broth is below the levels needed to stabilize the plasmid; instead, stabilization is mediated by the Tn1331 resolvase acting at the res site (13,21). However, the efficiency of Xer-mediated dimer resolution at mwr is substantially increased when the cells are cultured in low-osmolarity broth (4,13). The low levels of dimer resolution observed when cells are cultured in L broth seem to be due to a weak interaction of the substandard mwr ARG box with ArgR, hindering proper formation of the synaptic complex.…”